The present invention relates to a monitoring apparatus and method particularly useful in photolithographically processing of substrates, particularly useful in the manufacture of semiconductor devices,
The principal process of production of semiconductor devices is photolithography, which includes three main serial steps or operations:
(a) coating a semiconductor wafer with photoresist material (PR);
(b) exposing the PR through a mask with a predetermined pattern in order to produce a latent image of the mask on the PR; and
(c) developing the exposed PR in order to produce the image of the mask on the wafer.
The satisfactory performance of these steps requires a number of measurements and inspection steps in order to closely monitor the process.
Generally speaking, prior to a photolithography process, the wafer is prepared for the deposition of one or more layers. After a photolithography process is completed, the uppermost layer on the wafer is etched. Then, a new layer is deposited in order to begin the aforementioned sequence once again. In this repetitive way, a multi-layer semiconductor wafer structure is produced.
FIG. 1 schematically illustrates a typical set-up of photocluster tools of the photolithography process in a semiconductor fabrication plant (Fab). The photocluster (or link) is composed of two main parts: a phototrack 5, and an exposure tool 8. The phototrack includes a coater track 6 having a cassette load station 6a, and a developer tack 10 having a cassette unload station 10a. Alternatively, both coater and developer functions may be combined and realized in the same stations (not shown). The wafer W is placed in the cassette station 6a. From there, the wafer is loaded by a robot 2 to the coater track 6, where the coating step (a) commences. After step (a), the wafer is transferred by the robot 2 to the exposure toot 8, where the exposing step (b) is executed. Here, using optical means installed inside the exposure tool, the pattern on the mask is aligned with the structure already on the wafer (registration). Then, the wafer W is exposed to electromagnetic radiation trough the mask. After exposure, robot 2 transfers the wafer to the developer track 10 where the micro-dimensional relief image on the wafer is developed (step (c)). The wafer W is then transferred by robot 2 to the cassette station 10a. Steps (a)-(c) also involve several different baking and other auxiliary steps which are not described herein.
As shown in FIG. 1, the coater track 6, the exposure tool 8, and the developer track 10, are tightly joined together in order to minimize process variability and any potential risk of contamination during photolithography, which is a super-sensitive process. Some available commercial exposure tools are series (MA-1000, 200, 5500) of Dainippon Screen MFG. Co. Ltd., Kyoto, Japan, PAS-5500 series of ASM Lithography, Tempe, Ariz., series FPA 3000 and 4000 of Canon USA Inc., USA, and Microscan of SVGL, Wilton, Conn. Some available phototracks are series 90s and 200 of SVGT, San-Jose, Calif., Polaris of FSI International, Chaska, Minn., and phototracks D-spin series (60A/80A, 60B, 200) of Dainippon Screen MFG. Co. Ltd., Kyoto, Japan, Falcon of Fairchild Technologies Inc., USA and of Tokyo Electric Laboratories (TEL.), Japan.
It is apparent that in such a complex and delicate production process, various problems, failures or defects, may arise or develop during each step, or from the serial combination of steps. Because of the stringent quality requirements, any problem which is not timely discovered may result in the rejection of a single wafer, or of the entire lot.
In modem photolithography processing, especially using DUV exposure, a wafer cannot be taken out of the photocluster for measurement or inspection before the process is completed and the wafer arrives at the cassette station 10b. As a result, any process control based on measuring processed wafers cannot provide xe2x80x98real timexe2x80x99 process malfunction detection. Therefore, there is an urgent need for an approach based on integrated monitoring, i.e., a monitoring apparatus physically installed inside or attached to the relevant production unit, dedicated to it, and using its wafer handling system. Such integrated monitoring can provide tight, fast-response and accurate monitoring of each of the steps, as well as complete and integrated process control for the overall semiconductor production process, in general, and for photolithography, in particular.
However, the existing monitoring and control techniques typically utilize xe2x80x98stand-alonexe2x80x99 monitoring systems. A xe2x80x98stand-alonexe2x80x99 monitoring system is installed outside the production line, and wafers are transferred from the production unit to this system using a separate wafer handling arrangement than that of the production process.
In general, three different monitoring and control processes are performed at the present time during semiconductor fabrication process. These are monitoring of (a) overlay registration, (b) inspection and (c) critical dimension (CD) measurement. A brief description of each of these processes is given below:
The overlay registration (hereinafterxe2x80x94xe2x80x9coverlayxe2x80x9d) is a process executed in the exposure tool 8 in which the pattern on the mask is aligned with respect to the pattern features existing already on the uppermost layer on the wafer. The shrinking dimensions of the wafer""s features increase the demands on overlay accuracy.
An overlay error or misregistration (hereinafterxe2x80x94xe2x80x9coverlay errorxe2x80x9d) is defined as the relative misalignment of the features produced by two different mask levels. The error is determined by a separate metrology tool from the exposure tool.
FIG. 2A illustrates a typical overlay error determination site on a wafer. It is composed of two groups of target lines, one on the uppermost feature layer of the wafer 11 and the second is produced on the new PR layer 16. Target lines 16 are similar but smaller than target lines 11; thus they can be placed in the center of target lines 11. Therefore, these overlay targets are called xe2x80x9cbars in barsxe2x80x9d. FIG. 2B is a top view of the same overlay error determination site. The lines of these targets, such as 11a and 16a are typically of xcx9c2 xcexcm width, and 10-15 xcexcm length, respectively.
According to a common method, the overlay error is defined as the relative displacement of the centers of target lines 11 with respect to lines 16, in both the X- and Y-axes. For example, in FIG. 2B the displacements between lines 11a and 16a, 11b and 16b are denoted as 14a and 14b, respectively. Thus, the overlay error in the X-axis is the difference between the lengths of lines 14a and 14b. 
FIG. 3 illustrates a common configuration of photocluster tools and a xe2x80x98stand-alonexe2x80x99 overlay metrology system composed of a measurement unit and an analysis station. It should be noted that wafers to be examined are taken out of the photolithography process-line, and handled in the measurement tool. This is associated with the following features of the available overlay technology: (i) closed loop control in xe2x80x98real timexe2x80x99 is impossible; (ii) not all the wafers as well as all the layers within a wafer are measured for overlay error; (iii) additional process step is needed; and (iv) a xe2x80x98stand alonexe2x80x99 tool is needed. It should be noted that it is a common situation in the Fab, especially in advanced production processes, flat during xe2x80x98stand alonexe2x80x99 overlay measurement, the processing of the lot is stopped. This break may even take a few hours.
The results of the measurements are sent to the analysis station, and a feedback is returned to the stepper in the photocluster tool.
U.S. Pat. No. 5,438,413 discloses a process and a xe2x80x98stand-alonexe2x80x99 apparatus for measuring overlay errors using an interferometric microscope with a large numerical aperture. A series of interference images are at different vertical planes, and artificial images thereof are processed, the brightness of which is proportional to either the complex magnitude or the phase of the mutual coherence. The differences between synthetic images relating to target attribute position are then used as a means of detecting overlay error. KLA-Tencor, Calif., the assignee of this patent, sells a xe2x80x98stand-alonexe2x80x99 machine under the brand name KLA-5200. In this system, the measurement and the analysis station are combined together.
U.S. Pat. No. 5,109,430 discloses another overlay metrology system. By comparing spatially filtered images of patterns taken from the wafer with stored images of the same patterns, the overlay error is determined. Schlumberger ATE, Concord, Mass., the assignee of this patent, supplies a xe2x80x98stand-alonexe2x80x99 machine for submicron overlay under the brand name IVS-120.
Other xe2x80x98stand-alonexe2x80x99 overlay metrology systems are manufactured by BIO-RAD micromeasurements, York, Great Britain, under the brand name Questar Q7, as well as by Nanometrics, Sunnyvale, Calif. (Metra series).
All the aforementioned methods and metrology systems for determining overlay error suffer from several drawbacks including the following:
1) They are all xe2x80x98stand-alonexe2x80x99 systems, i.e., operating off-line the photolithography process. Hence, they provide post-process indication of overlay errors, not during the production process itself, or before a batch of wafer production is completed. In some cases this may take hours, or more.
2) They result in a waste of wafers, and/or lots of wafers because of this post-process response. This results from the continuous operation of the photolithographic process on the one hand, and the time-delay from the time a wafer is sent off-line to overlay measurements until a response about an error is obtained, on the other band.
3) Usually, one of the main overlay error sources is the first mask alignment for a wafer to come on a lot. Such an error source cannot be corrected later since the error varies for each lot. For this reason it is important to have the feedback within the time frame of the first wafer which cannot be obtained using a xe2x80x98stand-alonexe2x80x99 tool.
4) The overlay sampling frequency is limited due to contamination restrictions and additional expensive time needed for extra handling and measurements.
5) Throughput of the photolithography process is reduced as a result of the post-process overlay detection and the long response-time, as well as of the reduced sampling frequency mentioned in (3).
6) These stand-alone systems require additional expensive foot-print and labor in the Fab.
7) The microlithography tools are the xe2x80x9cbottle neckxe2x80x9d in the semiconductors production process and they are the most expensive tools in the FAB. Their partial utilization due to late off-line measurements reduces drastically overall equipment efficiency in the Fab.
Inspecting during the production of semiconductors wafers can be defined as a search for defects caused by:
(a) contamination (dirt, particles, chemicals, residues, etc.), and/or
(b) process induced failures related to PR, coating, baking, development, handling, etc.
In order to detect defects originating only from the lithography process, a specific inspecting step is conducted after the development step as illustrated in FIG. 4. It is usually called xe2x80x9cafter development inspectionxe2x80x9d (ADI), or xe2x80x9cpost-development checkxe2x80x9d (PDCK). The present invention is mainly relevant for ADI.
In general, data obtained during the inspecting is analyzed, and in case an increased defects level is detected, an alarm is sent to the engineering level or to the production line. Once again it should be noted that, as in the case of overlay metrology, with the current technology, the ADI is located out of the production line; i.e., wafers to be inspected are taken out of the production process and handled in a separate inspecting station. It should also be noted that it is a common situation in the Fab, especially in advanced production processes, that during xe2x80x98stand alonexe2x80x99 inspecting, the processing of the lot is stopped. This break may take even few hours.
Today, the majority of ADI activities are non-automatic visual inspecting conducted by humans. In particular, no integrated automatic ADI system is commercially available at the moment.
ADI is aimed at:
(i) Coarse inspectingxe2x80x94A wafer is handled by hands and is visually inspected by eye-sight for large defects. These defects can be, for example, poor spinning during coating, poor development, scum, non-attached PR (xe2x80x98liftingxe2x80x99), and/or edge beads. This method can usually only detect defects bigger than tens of microns.
(ii) Fine inspectingxe2x80x94predetermined sites or targets on a wafer are visually inspected with the aid of a microscope (20-50xc3x97magnification).
These defects can be, e.g., shorts between conducting lines, and focus failures of the stepper.
ADI conducted by humans has several disadvantages:
(a) It is tedious and requires great concentration to locate pattern discrepancies in repetitive and complex circuits.
(b) The results are not uniform with respect to each inspector as well as between different inspectors. This point becomes crucial when considering the increased importance of inspecting at times when the wafer features become more and more delicate due to the continuous shrinking of the wafer""s features.
(c) It is not a consistent means for statistical analysis and for measuring process quality due to non-repetitive results.
(d) Additional costs due to the labor.
(e) Non objective inspecting, neither in defects identification nor in the specific action which should take place once a specific defect is identified.
(f) Fluctuating throughput results, among other things, in difficulties to determine sampling frequency.
(g) Manual inspecting is also done off-line and therefore suffers from all the same aforementioned disadvantages of xe2x80x98stand-alonexe2x80x99 systems.
To complete the picture, it should be noted that two automatic optical inspection (AOI) methods for defect detection are known, but their high cost and low throughput limit their use in actual production.
(i) Absolute methodsxe2x80x94illuminating a wafer at a predetermined angle (xe2x80x9cgrazingxe2x80x9d) and collecting the reflected signal from the wafer""s plane. Any signal above a threshold (absolute) value is determined as a defect. According to this method, particles bigger than 0.1 xcexcm can be detected.
(ii) Comparative methodsxe2x80x94these are divided into xe2x80x98die to diexe2x80x99 and xe2x80x98die to databasexe2x80x99. A wafer is photographed and then an automatic comparison of pixels in one die is made with respect to the correlative pixels in a neighbor die, or to a database. Usually, the result of the comparison should fit a set threshold, unless there is a defect. The threshold may be a function of the gray level and/or the specific location of the dye in the wafer.
Method (ii) overcomes the shortcomings of method (i), and usually detects defects such as dirt particles ( greater than 0.1 xcexcm), bridging of conducting lines, missing features, residues of chemicals and PR, etc. The defect level these methods can detect is determined according to the design rule of the industry (e.g., 0.1 xcexcm).
None of the available inspecting tools samples each wafer, but only several wafer in a lot. Moreover, the lack of such inspecting systems prevents any option for automatic and tight feedback or closed loop control over the lithography process. Thus, any serious attempt for establishing or even improving the process control around the photolithography process is prevented, or at least is met with crucial obstacles due to the lack of such method(s) and systems.
A third monitoring and control process is the Critical Dimension CD control which includes measurements of characteristic dimensions in critical locations on a wafer, e.g., widths of representative lines, spaces, and line/space pairs on the wafer. CD metrology tools are based on two main technologies: the CD scanning electron microscope (CD SEM), and the atomic forced microscope (CDAFM). Commercial tools based on CD SEM are series 7830XX of Applied Materials, Santa Clara, Calif., and DEKTAK SXM-320 of VFEFCO, USA is based on AFM.
FIG. 5 illustrates common configurations of xe2x80x98standalonexe2x80x99 CD tools with the production process. Typically, CD measurements take place after the developing step and/or after etching. The CD tool is located out of the production line, i.e., wafers to be measured are taken out of the production process and handled to a separate CD station. It should be noted that it is a common situation in the Fab, especially in advanced production processes, that during xe2x80x98stand alonexe2x80x99 CD measurement, the processing of the lot is stopped. This break may take even few hours.
In general, data obtained during the CD measurement is analyzed, and then a kind of feedback (or alarm in a case of a width out of the permitted range) is sent to the relevant unit in the production line.
CDSEM and CDAFM allow CD measurement for line/space width below the resolution limit of optical microscope. However, when possible, optical CD (OCD) measurement may be very useful because they can be combined with optical overlay measurement systems. Recently, (C. P. Ausschnitt, M. E., Lagus (1998) Seeing the Forest for the Trees: a New Approach for CD Controlxe2x80x9d, SPIE, vol. 3332, 212-220), it was proposed to use OCD even for sub-micron design rules that is behind the optical resolution. The idea is that optical systems allow fast measurement of many lies simultaneously. Statistical treatment of multiple measurements with low accuracy, allows to extract such important manufacturing data as repeatability or deviation trends.
It is clear, as was noted before with respect to overlay metrology and inspecting tools, that since all CD metrology systems are xe2x80x98stand-alonexe2x80x99 tools, they suffer from the same drawbacks as discussed before. Moreover, especially in the case of CD measurement, the results, e.g., line width, give a limited ability to correlate the measurement to any specific cause.
Overlay and CD monitoring can be performed in various levels in order to establish process control. The first common level is xe2x80x9clot to lot controlxe2x80x9d. In this method each lot is a basis for the next lot to run in this process. Small correction can be made by considering the results of the previous lot and making corrections. However a certain increment in the risk is introduced because a total lot may be lost.
A second control level is xe2x80x9csend ahead waferxe2x80x9d. In this method a pilot wafer is sent through the coating-exposure-developing steps, exposed in the recommended exposure, and is then sent to CD measurement. Satisfactory results will be a basis for the set up conditions of the lot, whereas unsatisfactory results will cause another wafer to be exposed with corrections for the exposure conditions. The over all sequence of a xe2x80x9csend ahead waferxe2x80x9d control can take many hours while valuable utility time of the production tools, as well as the production lot may be lost.
In some cases there is a need for a higher control level. This may be performed in a full process window mapping by running an exposure matrix, or focus exposure matrix, and analyzing the results. However, this is the most time-consuming method.
The drawbacks of these methods, when conducted with xe2x80x98stand-alonexe2x80x99 overlay and OCD tools, are that they are time and effort consuming and they usually do not respond directly for certain causes, or do not reveal any problematic sources. However, they make the xe2x80x9ctime to respondxe2x80x9d shorter as compared to long-term trend charts. Nonetheless, to enable a real feedback to problems, there is a crucial need for integrated monitoring of the process steps. The on-line measurements can respond directly to a certain cause with the correct straight forward correction action.
It should be emphasized that these problems with respect to process control xe2x80x98stand-alonexe2x80x99 systems are dramatically aggravated when considering the coming future developments in the semiconductor industry. Because of the shrinking critical dimensions of the wafer""s features, as well as the introduction of new and non-stable processes (e.g., DUV resist, and transition to 300 mm diameter wafer with corresponding restrictions on wafer handling), the need for an integrated monitoring and process control for semiconductors production becomes crucial. For this reason, traditional process control methods that use long-term trend charts, and which are xe2x80x9coffline methodsxe2x80x9d will be more and more excluded.
As noted before, integrated monitoring and process control systems are a reasonable solution for the above-discussed problem. However, such a system should be considered from several aspects and meet specific requirements in order to become real and feasible:
(a) Small footprintxe2x80x94such a system should have as small footprint as possible (practically not smaller tan the wafer size) in order to be physically installed inside the photocluster;
(b) Stationary waferxe2x80x94the wafer should be stationary during inspection and measurement to exclude extra wafer-handling and particles generation;
(c) High throughputxe2x80x94the system should have high throughput such as not to reduce the photocluster throughput;
(d) Cleanlinessxe2x80x94the measuring unit should not interfere in any way with the photocluster or introduce any potential risk of contamination;
(e) Access for maintenancexe2x80x94the system parts except the measuring unit (e.g., control electronics, light source), should be outside the photocluster in order to enable, among other things, easy and quick maintenance without any disturbance to the photocluster;
(f) Cost-effective the integrated tool cost should be a small portion of the phototrack cost.
xe2x80x9cStand-alonexe2x80x9d monitoring and process control systems do not meet these stringent requirements, and apparently cannot be used as an integrated system. Moreover, no such integrated system is now available on the market. Therefore, there is a need for a new monitoring and process control apparatus and method having advantages in the above respects.
An object of the present invention is to provide a novel apparatus and method having advantages in one or more of the above-described respects, particularly important in the photolithography processing of substrates, e.g., semiconductor wafers.
According to one aspect of the present invention, there is provided apparatus for processing substrates according to a predetermined photolithography process, comprising:
a loading station in which the substrates are loaded; a coating station in which the substrates are coated with a photoresist material;
an exposing station in which the photoresist coating is exposed to light through a mask having a predetermined pattern to produce a latent image of the mask on the photoresist coating;
a developing station in which the latent image is developed;
an unloading station in which the substrates are unloaded; and
a monitoring station for monitoring the substrates with respect to predetermined parameters of said photolithography process before being unloaded at the unloading station, said monitoring station comprising:
a supporting assembly for receiving substrates to be inspected;
a sealed enclosure having a transparent window aligned with and facing said supporting plate, said supporting plate being externally of said sealed enclosure and spaced from said window thereof; and
an optical monitoring system within said sealed enclosure for inspecting substrates on said supporting plate via said transparent window, wherein the optical monitoring system is associated with at least one light source and comprises a spectrophotometric measurement channel.
As will be described more particularly below, the optical monitoring system between the developing station and the unloading station may detect one or more of the following: (a) overlay registration errors; (b) inspection of substrates for defects in the photoresist layer (i.e., estimation of the quality of the PR pattern); (c) critical dimensional errors; (d) measurement of the substrate""s parameters (such as thickness of at least one layer of the substrate and/or optical parameters of at least one layer of the substrate).
In the described preferred embodiments, the at least one light source is externally of the sealed enclosure and produces a light beam which is applied to the optical system within the sealed enclosure.
In addiction, the optical monitoring system within the sealed enclosure includes an optical imaging device; and the monitoring station further includes a digital image processing unit accommodated externally of the sealed enclosure and connected to the optical imaging device by electrical conductors passing into the sealed enclosure.
The monitoring station further includes a central processing unit accommodated externally of the sealed enclosure and connected to the optical monitoring system for controlling the system via electrical conductors passing into the sealed enclosure.
According to still further features in the described preferred embodiments, the optical monitoring system within the sealed enclosure includes the following components: a low-magnification channel for aligning the optical inspecting system with respect to a patterned substrate on the supporting plate or for coarse inspection; and a high-magnification or high-resolution channel for measuring the predetermined parameters of the photolithography process after the substrate has passed through the developing station and before reaching the unloading station. The low-magnification channel and the high-resolution channel are fixed with respect to each other. These channels may be associated with separate light sources.
The spectrophotometric channel may utilize a separate optical system that may and may not utilize a separate light source. Such an optical system includes an objective lens, a beam splitter for separating incident light and light coming from the substrate, an imaging lens and a spectrophotometer. Alternatively, an optical system of the spectrophotometic channel may utilize an objective lens, a beam splitter and an imaging lens of the low-magnification channel.
According to another aspect of the present invention, there is provided a monitoring apparatus for optically monitoring articles, comprising:
a supporting plate for supporting the article to be monitored;
a sealed enclosure having a transparent window aligned with and facing said supporting plate, said supporting plate being externally of said sealed enclosure and spaced from said window thereof;
an optical monitoring system within said sealed enclosure for inspecting the article on said supporting plate via said transparent window, the optical monitoring system comprising a spectrophotometric channel; and
a light source for illuminating the article via said optical monitoring system, said light source being externally of said sealed enclosure and producing a light beam which is applied to said optical monitoring system within said sealed enclosure.
The invention also provides a novel method of processing substrates according to a predetermined photolithography process. The method comprises the following operations: coating the substrate with a photoresist material; exposing the photoresist coating to light through a mask having a predetermined pattern to produce a latent image of the mask on the photoresist coating; and developing the latent image; and is characterized in monitoring the substrate with respect to predetermined parameters of the photolithography process after the substrate has been developed, said monitoring including spectrophotometric measurements, and controlling said photolithography process in accordance with the results of said monitoring operation.
As will be described more particularly below, the invention permits one or more or the following to be provided:
1) An integrated apparatus for overlay metrology and/or inspection, and/or OCD measurements. Such an apparatus would have high accuracy and high throughput and could be physically combined inside the present foot print of photocluster tools; i.e., it would have a zero additional foot print on the production floor. The combination of up to three different functions in one tool would have its own advantages: (i) Better exploitation of utilization time xe2x80x94each inspecting, overlay and CD measurement could have its own sampling frequency and need not be the same for every wafer. Thus, such an apparatus could be continuously operated while its utilization time is shared between the three functions. (ii) A direct result from (i) is that the apparatus could drastically decrease the numbers of lots which would be simultaneously running around the production process as common today (one for overlay measurement, one for inspecting, one for CD, and one which begins the lithography process), (iii) Such apparatus could be client-oriented, i.e., could be exactly fitted to the customer needs as well as to changing needs. (iv) The apparatus could be oriented for a specific problem; (v) The apparatus could have a relatively low price.
2) An apparatus as in (1) which will not reduce the throughput of the photocluster by carrying out measurements/inspection in parallel with the processing of the next wafer.
3) A modular apparatus as in (1) capable to perform only overlay metrology or inspecting or OCD measurements with enhanced performance if needed.
4) An apparatus as in (1) combined with a processing unit, thus enabling to establish monitoring and process control based on overlay, inspecting and OCD measurements.
5) An integrated automatic inspecting system which is much more accurate, faster, and repetitive than visual inspecting conducted by humans.
6) A method for integrated monitoring and process control for overlay metrology and/or inspection and/or OCD within the photolithography production process, thereby enabling much shorter response times as compared to the common xe2x80x98stand-alonexe2x80x99 systems.
7) Methods which facilitate and dramatically shorten the time needed for common process control methods such as xe2x80x98send a wafer aheadxe2x80x99, xe2x80x98lot to lotxe2x80x99, etc.
8) A new and practical monitoring and process control method by means of xe2x80x98wafer to waferxe2x80x99. Such a method is practically impossible to conduct in the current situation of xe2x80x98stand-alonexe2x80x99 systems. However, with these new integrated methods, which do not decrease the throughput of the production process a tight, fast-responding, directly to cause, monitoring and process control method can be conducted. Apparently, in certain circumstances, this new method may save the need for separate and expensive xe2x80x98stand-alonexe2x80x99 systems for overlay metrology, inspection and OCD.
9) A method with which both overlay error, inspection and OCD can be determined either on one wafer of a lot or on different wafers in the same lot.
10) An integrated and elaborated inspecting monitoring and control system.
11) The process can be implemented in several alternative levels. One would be aimed at notifying the production process controller about defects in general. Another would be aimed at investigating the direct reasons and/or the induced failure which caused the defects. Then, a feedback would be directed, to any predetermined relevant point in the production process. By this, a feedback or a closed loop control can be established either for a single step in the production process (e.g., exposure step, post exposure bake (PEB)) or for the whole process when combined with other metrology system(s), such as overlay and/or critical dimension metrology systems.
Such a method and apparatus have the potential to save expensive utilization time (e.g., by shortening methods such as xe2x80x98send a wafer aheadxe2x80x99) as well as diminishing the amount of test wafers wasted during the production process.
In addition, there would be no need for additional wafer handling from or to the photolithography tools, thus saving utilization time as well as preventing additional contamination and wafer breakage.